Publicity domain having to include secure network (6)
I believe the answer is:
adland
'publicity domain' is the definition.
(adland means the advertising industry)
'to include secure network' is the wordplay.
'to include' becomes 'add' (I've seen this before).
'secure' indicates putting letters inside (inserted letters are secured inside).
'network' becomes 'LAN' (Local Area Network).
'add' placed around 'lan' is 'ADLAND'.
'having' acts as a link.
(Other definitions for adland that I've seen before include "ideal world?" , "commercial world" , "What urges people to buy" .)